This invention relates to security alarm systems, and more particularly to systems of this type which employ radio transmitters and receivers for the purpose of providing a signal when property or equipment is being stolen, vandalized or tampered with.
In the past many safeguard systems have been proposed and produced for protecting property against theft and vandalism. The wiring of windows and doors for the purpose of providing an alarm at a central surveillance station has long been in use. More recently, buildings have been wired and equipped with alarm systems, to foil intruders. These intruder alarms have in many instances involved the placement of electric, window and door switches which were wired to a common alarm apparatus that was continuously energized and in readiness for triggering. More recent and sophistocated alarm systems have also been devised, which involve the use of radio transmitter units that are actuated by magnetic operators, thereby elminating the necessity for installing wiring in walls, moldings, etc. which always is a time-consuming and costly procedure, as well as one which can impair the appearance of building interiors. With such installations, the radio transmitter comprised a small, self-contained unit that was fixedly attached to window or door framing and was triggered by movement of a magnetic piece secured to the window sash or door. These units required for their activation the association with a moving magnetic piece, and could be defeated if the window were to be broken and a jumper wire installed in the case of normally closed switches, or else if an alarm wire were to be snipped in the case of normally open switches. In the case of wired systems, an intruder could easily defeat the same by shorting or cutting those wires which lead from the trigger switches. In each instance of these known intruder alarms there existed the possibility of rendering the device inoperative by manipulating or modifying a part of the system at one point or another of the locale which is to be protected. So far as we are aware, no existing alarm system of whatever type has been completely or 100 percent tamper-proof, for the reasons mentioned above.